Comprehensive lists of the ranking systems for all five branches of the U.S. military, including the Marines, are published at Military-Ranks.org. The U.S. Marine Corps hierarchy consists of 27 unique ranks, from the entry-level private to the four-star general, which is the highest rank attainable.
The Marine Corps ranking structure, as with the rest of the U.S. military, is divided into three main categories: enlisted men, warrant officers and commissioned officers. Each rank is denoted by a unique insignia worn and displayed on the service member's uniform. As of 2015, there have been 65 four-star generals in the U.S. Marine Corps.